1. Field of the Invention
The present invention relates to a method for automatically coordinating flash intensity and camera system as the same, particularly to a method for automatically coordinating flash intensity in accordance with the distance, the luminance and other parameters.
2. Description of the Related Arts
Flash devices are usually equipped with digital cameras, which provide additional light while the objects are not illuminated enough. In operation, different flash modes are applied to adjust the flash parameters. A manual flash mode and an auto flash mode are known as two generally used flash modes. When the flash device is in a manual flash mode, the flash flashes immediately after a shutter curtain is fully opened. The parameters, such as flash intensity and flash duration, are set prefirst. When the object is in another different condition, for example, the distance between the object and the camera has increased, or the luminance of the object has decreased, the camera cannot coordinate itself according to the changes of environment, and the parameters are need to be manually adjusted. However, general customers without skilled technology cannot finish it, so most of the present cameras utilize the auto flash mode. In the auto flash mode, the camera calculates the distance that the objects apart from the camera and the luminance of the objects to coordinate the flash intensity and flash duration. The relationship between the parameters is given below:GN=A*L  (1)Where GN represents a guide number of the flash; A represents an aperture of the camera; L represents a distance objects against the camera. The GN is a certain scale for luminance that the flash has emitted, and it's an important parameter to estimate the performance of the flash. The unit of the GN is meter.
For measuring the distance from the object to camera, a distance measure unit and a photo-sensor unit are two kinds of generally used ways. The distance measure unit is a professional measuring instrument, which sends light to the object, calculates the flight time until it receives the reflected light, and multiplies the time to the speed that the light transmits, thereby working out the distance. Cameras with the distance measure units may precisely measure the distance, however, it's too expensive for general customers. Meanwhile, though the cameras with the photo-sensor unit to measure the distance will be much cheaper, it's much poor in precision. When operating, the flash pre-flashes, the camera receive the reflected light from the object, judge whether the object is illuminated enough. The camera compares a reference exposure value with the present and works out the distance that the camera against the object. Although the cameras with photo-sensor units to measure may be much cheaper than ones with distance measure units, a pre-flashing design may exhaust the power, which bring in another problem.
Therefore, it's essential to support a new method for the camera to adjust the parameters of the flash without above-mentioned shortcomings.